1. Field of the Invention
The present invention relates to an apparatus for measuring the amount of minute particles contained in pure water and other liquids used for washing and the like during a process for manufacturing integrated circuits.
2. Description of the Prior Art
Superpure water containing a very small amount of minute particles has been used for washing and the like in a process of manufacturing integrated circuits. A measuring apparatus as shown in FIG. 6 has been used as a measuring apparatus for measuring the amount of minute particles contained in liquids used as washing water in such process.
Referring now to FIG. 6, the apparatus has a parabolic reflecting mirror 61, an optical detector 62 provided at the focal point of said reflecting mirror 61 opposite said reflecting mirror 61 and to which all light emanating from an origin O is reflected, source of light 63, such as a tungsten lamp, arranged behind said reflecting mirror 61, a beam of light being incident upon said origin O of said reflecting mirror 61 through an optical system 64 and a passing-through hole 65 formed in said reflecting mirror 61. A glass tube extends through the origin O of said reflecting mirror 61 at right angles to said incident beam, said glass tube 66 being supplied with water the particle content of which is to be measured. A trap 67 is disposed between said glass tube 66 and said detector 62 for preventing the beam of light from said source of light 63 from reaching the detector 62 directly.
In the measurement of the amount of particles by this apparatus, a beam of light from the source of light 63 is irradiated on water, the particle content of which is to be measured, in the glass tube 66, and scattered light scattered by a particle is reflected by the reflecting mirror 61 to the detector 62, and the input to the detector being a measure of the number of particles contained in a unit volume of water.
With the above described conventional apparatus, since the beam of light is irradiated on water passing through the glass tube 66 and the number of particles is counted, some scattered light is produced in the glass tube 66 due to a difference between the refractive index of the glass in the tube 66 and that of the water, and this reaches the detector 62 as noise, and causes the S/N ratio to be bad. A problem also occurs that if the scattered light from the particles is weak, it is difficult to be detected apart from the scattered light from the glass tube 66, whereby the lower limit of the size of detectable particles is about 0.5 .mu.m, and the detecting accuracy is also low.